The configuration under host has the same parameters as the configuration from Adldap2.
The usernameAttribute set the field which you wanna map to your username in neos. roles defines the mapping on which group should display which Neos Role and the defaultRole acts like a fallback when either no mappings are defined or the user has no groups in ldap.
With the additionalHosts setting you cann define additional ldap servers, but be careful the more server the slower will be the authentication process. To add an additionalHost just add this: